Many aircraft, including large transport category aircraft, use various types of trailing edge flaps to increase wing area and/or wing camber during low speed and/or high angle of attack operations. The increased area and/or camber can provide improved performance (e.g., increased lift). Accordingly, these flaps can improve takeoff and/or landing performance. One such flap is a dropped hinge flap. The dropped hinge flap rotates about a hinge located below the chord line of the flap. Accordingly, as the dropped hinge flap extends, it increases the camber of the wing and also moves aft in a Fowler motion. This Fowler motion can increase wing area and create a gap between a trailing edge of the wing and a leading edge of the flap. The gap can allow high energy air from the bottom of the wing to energize lower energy air flowing over the top portion of the flap.
FIGS. 1A and 1B are partially schematic illustrations of a dropped hinge flap 40 installed on a wing 20 of an aircraft 1. FIG. 1A is a top plan view of the flap 40, the wing 20, and a portion of a fuselage 5 of the aircraft 1. In FIG. 1A, the dropped hinge flap 40 is positioned on a portion of the wing 20 where the leading and trailing edge of the wing 20 are both swept relative to the longitudinal axis of the fuselage 5 (e.g., swept relative to the X axis). Accordingly, the flap 40 is positioned so that it rotates between a retracted position (shown in solid lines) and an extended position (shown in ghosted lines) about a hinge line HL that is also swept relative to the longitudinal axis of the fuselage 5 (e.g., the flap can travel in a somewhat cylindrical motion). However, the lateral edges of the flap 40 and the surrounding structure of the wing 20 (including the edges of other control surfaces on the wing) run parallel to the longitudinal axis of the fuselage.
Because of the swept hinge line HL, as the flap 40 moves between the retracted and the extended positions, the lateral edges of the flap rotate in a plane that is non-parallel to the longitudinal axis of the aircraft. This can cause clearance problems between the flap 40 and the surrounding structure of the wing 20. Additionally, as illustrated in both FIGS. 1A and 1B, a gap GP can be created between a laterally adjacent control surface 85 that rotates to an extended position about a hinge line that is perpendicular to the longitudinal axis of the fuselage (e.g., a hinge line that runs parallel to the Y axis). Such a gap GP can create aerodynamic inefficiencies, which in turn can reduce lift benefits provided by the flaps and/or increase drag.